The use of endoscopes for diagnostic and therapeutic indications is rapidly expanding. To improve performance, endoscopes have been optimized to best accomplish their purpose. Therefore, there are upper endoscopes for examination of the esophagus, stomach, and duodenum, colonoscopes for examining the colon, angioscopes for examining blood vessels, bronchoscopes for examining the bronchi, laparoscopes for examining the peritoneal cavity, and arthroscopes for examining joint spaces. The discussion which follows will apply to all of these types of endoscopes.
Instruments to examine the rectum and sigmoid colon, known as flexible sigmoidoscopes, are good examples of the usefulness of this endoscopy technology. These devices are expensive, used in contaminated environments for a procedure which is brief (5-10 minutes), and where problems of cleaning time and contamination are important factors. There has been a large increase in the use of the "flexible sigmoidoscope" for use in screening symptomatic and asymptomatic patients for colon and rectal cancer. Ideally, flexible sigmoidoscopes must be used frequently and inexpensively in order to maintain the cost of such screening at acceptable levels. Typically, a clinic would like to perform five to ten sigmoidoscope examinations each hour. One significant problem with making such frequency of examinations inexpensive is the time necessary for adequately cleaning the device. While external surfaces of endoscopes can be adequately cleaned, endoscopes typically have air, water, biopsy, and suction channels extending along their length which come into contact with bodily tissues or fluid. It is extremely difficult to adequately clean these channels even when skilled health practitioners spend a great deal of time on the cleaning procedures. Accordingly, conventional endoscope cleaning techniques greatly increase the cost of endoscopic procedures.
One approach to the endoscope contamination problem is described and claimed in U.S. Pat. No. 4,646,722 to Silverstein et al. The Silverstein et al. patent discloses the use of a flexible elastomeric sheath that surrounds the insertion tube of an endoscope. The distal end portion of the sheath includes a transparent window that covers a viewing window at the distal end portion of the insertion tube. The sheath also includes one or more channels that extend through the sheath adjacent to the insertion tube to allow endoscopic procedures to be performed without contaminating the endoscope itself. Once a procedure has been completed, the sheath, including its channels, is removed from the endoscope thus leaving the endoscope free to perform additional procedures without cleaning or disinfecting. The approach described in the Silverstein et al. patent has provided a great improvement in the ability to efficiently conduct endoscopic procedures without either the risk of contamination or the expense of a thorough cleaning and disinfecting between the procedures.
Traditional endoscopes have an insertion tube constructed of a vinyl or urethane covered spring connected to an articulating section comprised of metal vertebrae covered with a rubber material. This insertion tube construction gives the required axial and torsional rigidity for most of the length of the endoscope along with a more flexible articulating section which can be moved with little applied force in a relatively tight bending radius. The placement of a tight fitting sheath surrounding the insertion tube, although it is needed for the length of the insertion tube, can detrimentally inhibit mobility, control, and flexibility at the articulating section.
Installation and retention of the sheath on the endoscope are important procedures that must be completed with care to ensure that the distal end portion of the insertion tube is properly positioned at the distal end portion of the sheath for proper visibility through the window at the distal end portion of the endoscope. Sheaths have been installed on endoscopes using an inflation procedure, as is taught in U.S. Pat. No. 5,419,310, wherein the elastomeric sheath is inflated to an expanded position, and the endoscope's insertion tube is inserted into the sheath. After the insertion tube is properly positioned in the sheath, the sheath is deflated so that it contracts onto the insertion tube. A problem with the use of a flexible elastomeric sheath, such as latex, is that longitudinal as well as radial expansion of the sheath occurs upon inflation, and such expansion can leave a loose or baggy distal end portion as the sheath deflates, particularly if it deflates toward the proximal end portion first. The baggy distal end portion of the sheath is a problem because the transparent window in the sheath's distal end portion can be easily improperly positioned relative to the endoscope's viewing window, which can result in glare and poor visibility.
A further drawback and problem encountered during installation of the insertion tube into the sheath is ensuring a secure connection between the distal tip of the endoscope and the distal tip of the sheath. Differential lengths of the sheath as compared to the insertion tube have been used to keep the distal end portions of the scope and sheath in adjacent proximity by stretching the sheath so as to pull the distal end portion of the sheath against the distal end portion of the tip. This procedure of using differential lengths is known as preloading. However, preloading is typically not satisfactory when the sheath includes working channel for the passage of endoscopic accessories or other instrumentation. The force required to pass a tool through the working channel, particularly when the channel is bent about a tight radius, is sometimes sufficient to dislodge the distal tip of the sheath from the distal tip of the insertion tube. Thus, the viewing window in the sheath is displaced from the distal end portion of the insertion tube and causes glare or focus problems at the imaging lens in the insertion tube's distal end portion.
Another drawback of preloading is an increase in the force required to articulate the endoscope due to additionally stretching the already preloaded elastomer employed in the sheath construction. U.S. Pat. No. 5,477,148 teaches the use of an endoscope with a sheath having an end cap that engages the distal-end portion of the endoscope's insertion tube with seal members that provide a detent engaging the insertion tube. These detents ensure that the distal tip of the sheath and the distal end portion of the insertion tube remain locked together during the endoscopic procedure. In addition, the force required to articulate the sheathed insertion tube is reduced, because installation of the sheath requires less stretching and reduced preloading for retention of the sheath on the insertion tube.
However, the drawback of utilizing these detents is that the distal end portion of the sheath must be manually installed and removed. Generally, some level of expertise is required to successfully execute the installation and removal procedure. In addition, the unsnapping of the sheath's distal end portion from the insertion tube typically requires that a contaminated distal end portion of the endoscope be grasped by a user to disengage the sheath, often resulting in contamination of the user's hand(s). Such contamination of the user's hand(s) is then problematic, due to the risk of the user contaminating other instrumentation, equipment, personnel, or the like.